Slot type antenna having an autotransformer coupling circuit



R. A. DAVIS SLOT TYPE ANTENNA HAVING AN AUTOTRANSFORMER COUPLING CIRCUITFeb..7, 1961 2 Sheets-Sheet 1 Filed July 18, 1955 ROSS A. DAVISINVENTOR.

FIG-1- FIG-6- HIS ATTORNEY Feb. 7, 1961 R. A. DAVIS 2,971,191

SLOT TYPE ANTENNA HAVING AN AUTOTRANSFORMER COUPLING CIRCUIT Filed July18, 1955 2 Sheets-Sheet 2 BIB 108 'no 700 r IN V EN TOR.

ypiw XM HIS ATTORNEY United States Patent SLOT TYPE ANTENNA HAVING ANAUTO- TRANSFORMER COUPLING CIRCUIT Ross A. Davis, 5037 W. Pico Blvd.,Los Angeles, Calif.

Filed July 18, 1955, Ser. No. 522,777

6 Claims. (Cl. 343-712) This invention is directed totransmitting orreceiving antennas for structures and, more particularly, to lowimpedance antenna systems actively utilizing radio frequency currentsflowing along the conductive boundaries surrounding discontinuities inthe structures, be they mobile or fixed structures.

The invention covered herein differs from that covered in my co-pendingapplications, Serial No. 487,535, filed February 11, 1955, and entitledAntenna Systems, now Patent No. 2,923,813, issued February 2, 1960, andSerial No. 503,190, filed April 22, 1955, and entitled Antenna Systems,in that the structure and circuitry of the present invention insure anover-all maximum gain for the antenna system.

7 Therefore, it is an object of this invention to provide an improvedradio receiving or transmitting anntena exhibiting a low impedancecharacteristic and utilizing as an active component a large mass ofmetal normally per forming other functions.

It is a further object of this invention to provide a hidden antennasystem for mobile vehicles which provides optimum electromagnetic signalinterception and translation to associated receiving or transmittingequipment while simultaneously providing a high degree ofomnidirectivity and a minimum of electrostatic noise interception.

According to the present invention, currents which have been found toflow about the perimeter of any discontinuity in a conductive mass, suchas window openings in car bodies, are coupled through novel voltagetransforming coupler arrangements adjacent to or removed from at least aportion of the perimeter of any such discontinuity or opening to theantenna input or output circuits of associated radio apparatus. Theinductive component of the coupler impedance is offset by the insertionof at least one capacitor in the coupler arrangement. Circuit parametersare chosen ,so that the coupler arrangement will be series resonant, andthus exhibit a minimum impedance, at or near the low end of thefrequency band of the associated radio apparatus.

The features of the present invention which are be lieved to be novelare set forth with particularity in the ap pended claims. The presentinvention, both as to its organization and manner of operation, togetherwith further objects and advantages thereof, may best be understood byreference to the following description, taken in connection with theaccompanying drawings, in which:

Figure 1 is a diagrammatic presentation of a first and basic embodimentof the invention applied to an automobile.

Figure 2 is a second embodiment of the present invention in which theauto-transformer coupling member is disposed adjacent to the perimeterof a discontinuity in a conductive mass, such as a window opening in anautomobile.

V Figure 3 is a third embodiment of the present invention in which theauto-transformer coupling member is "ice removed from the general areaof the discontinuity and pick-up leads.

Figure 4 is a sketch of a fourth embodiment of the present invention inwhich the auto-transformer portion of the coupling circuit is contiguouswith at least a portion of the discontinuity in the conductive mass.

Figure 5 displays the embodiment of Figure 4 (with other embodimentsequally applicable) as may be conveniently series coupled to the tuningportion of a first R-F amplifier.

Figure 6 is a representation of a sixth embodiment of the presentinvention in which the principal auto-transformer member is located in aremote place with respect to the discontinuity of a conductive mass andin which the output leads are adapted for series coupling between thecapacitor and the inductor of the tuning portion of an R-F preselector,for example.

Figure 7 is a sketch of a modification of the embodiment shown in Figure6 in which separated, non-planar portions of the conductive mass areutilized for signal detection.

Figure 8 is a diagram of an additional embodiment of the presentinvention in which a complex form of autotransformer is driven byoppositely phased sources and a single output lead is used.

Figure 9 is a pictorial representation of the embodiment shown in Figure7, in simplified form, in which a signal from remote points is combinedwith a signal from an opening to provide high sensitivity and increasedan gular displacement from other signals derived from th same opening.

Figure 10 is a diagram of a modification of the-embodiments of Figures 7and 8. e

In Figure 1 window 10 delineates the discontinuity in" a conductive masssuch as an automobile body of which window frame 11 is a portion. As aresult of the electro-- magnetic fields which are constantly passingover the surface of the car body, currents are caused to flow in theconductive portions of the automobile body immediately surroundingWindow opening 11. This current flow is also present in window frame 11since it is assumed to be an integral portion of the car body itself;

point 13 of window frame 11 by means of conductor 23. Point 26 of sheath18 is electrically connected to' point 13 on window frame 11. Outputcoaxial cable 21 is subsequently routed to the input of the receivercircuitry (not shown).

. The circuit of Figure 1 operates as follows, using instantaneouspotentials in illustrating the analysis. A positive increment in thepotential at point 12 on window frame 11 will be followed by acorresponding positive increment in the potential at junction 27 ofconductors 16 and 19 and hence a positive potential increment atjunction 27 relative to point 17 upon conductive sheath 18 will beexperienced. Also, there will exist a slight positive potential at point25 relative to point 13. The positive voltages induced in conductor 19within sheath 18 and in the region within ferrite sheath 24 adjacentconductor 16 will add to the positive potential at point 12 to providefor an increased potential difference between conductor 19 and shielding22, i.e., at output coaxial" cable 21. This voltage rise will add to thevoltage rise" experienced at the juncture of conductors 16 and 19 so asto provide a further. increased voltage between shielding 22 of coaxialcable 21 and the inner conductor ficonductor 19).

so ast'o counteract the appreciable inductance inthe coupling circuit.One is not precluded from employing additional loops of conductor19'through sheath 18 provided the size of capacitor 15 is alsochanged tocounter= act the load change resultingfrom the increased loops.Foroptimum performance the coupling circuit in this particularapplication should be series resonant at or near the low end of thefrequency band. It should also be mentioned that conductor14 may beshielded with ferrite metal in the neighborhood of window 10 in this'andother embodiments if desired.

In Figure 2 the periphery ofwindow 200 is in part bounded by conductivesheath 201. Points 202 and 203 on conductive sheath 201 are respectivelycoupled to points 204 and 205 on window frame 206, these latter pointsbeing. assumed to exhibit a. potential difference therebetween.Conductor 207 is directly connected to point 204-n window frame 206 andloops through con' ductive sheath 201 toconnect to capacitor 208.Conductor 209 joins impedance lowering capacitor 208 at junction 216 andpoint 210 on conductive sheath 201. Con-- ductor 211 joins withconductor 209 and loops through the lower portion of sheath 201 a chosennumber of timesto emerge as inner conductor 212 of coaxial cable 213.Coaxial-cable shielding 214 is directly connected to window frame 206 inthe region of point 205.

The circuit shown in Figure 2 operates as follows. A potentialdifference existing between points 204 and 205 on window frame 206 as aresult of the passage of electromagnetic waves over the associated carbody is applied to points 202 and 203 at either end of conductive sheath201. Conductive sheath 201, its inner wire 207 and inner wire 209 offerrite sheath 215 operate as the primary of an auto-transformer member,the secondary comprising inner conductors 211 and 212. As a resultofithe action of conductor 207 and condenser 208, a potential differencewill exist between junction 216 and point 203 in the primary. As. aresult of auto-transformer action, the potential difference betweenpoint 203 and junction 216 will appear as an increased potential betweeninner wire 212 and outer sheath 214 of coaxial line 213. The outside ofthe lower portion of conductive sheath 201 is magnetically shielded fromexternal influences by ferrite sheath 215 which also increases theinductive reactance of the conductors passing therethrough. Impedancelowering capacitor 208 is inserted in series in conductor 207 (or othersuitable place) so as to provide a high output driving voltage at outputcoaxial cable 213 and maintains as low a primary impedance as ispossible. Output coaxial cable 213 is adapted for coupling to the inputof associated radio circuitry.

InFigure 3, conductive sheath 300 surrounds a portion of the peripheryof window 301 which is bounded by conductive window frame or boundary302. Again, window frame 302 is considered as the other window frames orboundaries in the previous figures, that is, being electrically integralwith the conductive mass or car body associated therewith. Points 303and 304 on window framev 302 are electrically connected to points 305and 306,-respectively,fon the periphery'of conductive sheath 300. Topoint 304 is electrically connected conductor 326'which.upo1r.'passingthrough conductive sheath 300' and: through coaxialcshield 307 iscoupled through condenser 311: to point-308'. Point 303 on window'frameIt has-been discovered that" in additionto increasing the impedance andcoupling coefiicient'o'f 302 is directly coupled through coaxial shield307 via conductor 310 and through capacitor 312 to point 309. It is tobe noted that an initial auto-transformer action is achieved by reasonofthe disposition of conductor 326 within conductive sheath 300 so that apotential difference greater than that between points 303 and 304 willappear between points 308 and 309; Impedance lowering capacitors 311 and312, respectively are electrically connected to the other portions ofthe primary313 and 318 in the ferrite sheath. The other endsofconductors 313 and 318 are electrically connected'through conductor317 to coaxial cable outer shield 314. The secondary 315 is joined tocapacitor 312 at point 309 whichis inductive- 1y coupled with conductors313 and 318 and which emerges as the inner conductor of output coaxialcable 316, of which shield 314 is a component part. Ferrite sheath 319encloses and thereby increases the inductive reactance and isolation ofconductors 313, 315 and 318. Condensers 311 and 312 are used to lowerthe primary impedance.

The embodiment shown in Figure 3 operates as follows. Initialauto-transformer action is supplied by the cooperation of conductiveshield 300 and conductors 310-and 326. Coaxial shield 307 maybe of aconventional variety, or may accomplish the magnetic shielding of theconductors enclosed therein by consisting of a ferrite sheath.Capacitors 311 and 312 are placed in series with the feed-in lines so astolower the over-all inductive imsome applications theinductive-capacitive characteristic of the coupling circuit should beresonant at a pointclose to the low end of the frequency band. Byvirtueof the unique winding of conductor 315, conductor 318, and conductor 313and their mutual inductive coupling therebetween a second and additiveauto-transformer action takes place which further serves to increase theoutput voltage derived at output coaxial cable 316. Conductor 317couples conductors 313 and 318 to outer coaxial shield 314 andconsequently provides a center tap. for this second auto-transformercircuitry.

The embodiment shown in Figure 4 is one of. the simplest types. Window400 is bounded by window frame 401 which is conductive in character andwhich forms an integral part of the conductive car body associatedtherewith. Points 402 and 403 along window frame 401 are each coupled topoints 404 and 405, respectively, at either end of conductive sheath406. Conductor 407 is electrically connected to point 402 along windowframe 401 and loops through conductive sheath 406 a chosen number oftimes to emerge therefrom and couple through capacitor 408 to finallyconstitute inner conductor 409 of output coaxial cable 410. Outercoaxial shield 411 is electrically connected to conductive sheath 406 ator near point 405.

The circuit of Figure 4 operates as follows. By virtue of a potentialdifference which exists or may exist between points 402 and 403 alongwindow frame 401, and consequently between points 404 and 405 alongconductive sheath 406 an in-phase voltage will be induced in eachsuccessive winding of conductor 407 through conductive sheath 406 toprovide an increased voltage difference between inner conductor 409 ofcoaxial cable 410 and shield 411. Again, capacitor 408 is utilized tocounteract the increased inductive impedance contributed to the couplingcircuit by reason of the successive loops of'conductor 407 throughconductive sheath 406'. Similar:

ly, the capacitance exhibited by capacitor 408 could be such in certainapplications as to provide for the series resonant condition of thecoupling circuit near the low end of the frequency band.

The circuit of Figure 5 is identical in configuration and operation as.the circuit of Figure 4', but does illustrate the fact that theimpedance reducing coupling capacitor may be'included within the inputcircuit of the associated receiver 'or radio apparatus itself. Inductor500 and tuning capacitor 501 comprise the normal tank circuit elementsof a conventional R-F preselector stage. The condenser or the inductanceor both can be variable to meet maximum tuning range requirements whenusing several turns in the pick-up inductance. By virtue of theinclusion of capacitor 502 in the input circuitry of the R-F preselectorthe exciter and coupling circuitry can be and is series-coupled betweeninductor 500 and capacitor 501. For best tracking, the coupling circuitincluding capacitor 502 may be made series resonant near the low end ofthe band. Also, with this arrangement the LC ratio of the receiver inputtank circuit will not be so greatly disturbed. It is interesting to notethat capacitor 502 also serves to keep the automatic volume controlvoltage from being shorted out to ground. The inclusion of shielding 503(made of ferrite material if desired) for housing conductor 504 andthereby holding down its impedance and shielding it from externalelectrostatic impulses in the neighborhood of window 505 is optionalboth in the case of the embodiment shown in Figure 5 and in all otherembodiments heretofore or hereafter shown and described.

The embodiment shown in Figure 6 is similar to those heretoforementioned with the exception of the presence 'of two final output leadsand also the unique autotransformer arrangement which is enclosed bydotted lines 600. Either coupling capacitors 601 and 602 or capacitors603 and 604, or both'sets of capacitors, may be employed to counteractthe inductive impedance exhibited by the coupling circuit. Coaxialshields 605 and 606 may be intercoupled and grounded as shown. Capacitor602 is coupled via conductor 607 to point 608 on conductive sheath 609.Capacitor 602 is also coupled via conductor 610 to coaxial cable 611 ofwhich shield 605 is a member. Capacitor 601 is coupled via conductor 612to join with conductor 607 at point 622 which in turn joins to point 608on sheath 609. Conductor 613 joins with capacitor 601 at point 624 andfinally emerges from the auto-transformer portion as inner conduct-or614 of coaxial cable 615. Ferrite sheaths 616 and 617 surround theconductive wires as shown. As near critical coupling as is possible toattain and simultaneously maintain reasonable capacity loading should bemade to exist between the center and two outer conductive wires withineach ferrite sheath 616 and 617.

The circuit shown in Figure 6 operates as follows. A sudden increase inpotential diiference between points 619 and 620 will appear as apotential increase between points 621 and 608 on conductive sheath 609due to the connection of conductive lead 618 and condenser 602 to wire607. Potentials of opposite polarity will exist between points 621 and622, and points 624 and 623, due to the action of additional conductivelead 625 running from point 619 through condenser 601 to point 624, sothat the current flow in conductors 607 and 612 will reinforce eachother. This means that voltages will be induced in the conductorsoneither side of each central conductor which in turn will he stepped upby the number of turns used in the autotransformer to finally appear atcoaxial cables 611 and 615 in opposite polarity on conductors 610 and614. It is interesting to note that the auto-transformer 600 may bedisposed either adjacent the car window or other associateddiscontinuity, or remotely from a discontinuity such as in the locationof the radio receiver. Also, it is not necessary that primaries 607 and625'have a return to a point such as 608. Experiment has shown thatremarkable signal detection may be achieved by the embodiment of Figure6.

The configuration of Figure 7 is identical to that of Figure 6 with theexception that a remotely situated driving point such as a point on atender well (point 700) may comprise one of the driving leads of thecircuit. If the potential at point 706 is increasing positively withrespect to point 707, and the potential at point 700 is increasingnegatively with respect to point 708 and such a condition exists atcondensers 701 and 702, the phasing will be correct for driving oppositelegs of the auto-transformer and attaining maximum output at the twooutput coaxi-als. This additional driving method was introducedprimarily to improve signal displacement between two points of pick-0Ein a common discontinuity when the angle of displacement in that openingis not sufiicient. If the driving voltages are properly phased, idealsignal conditions can be obtained through this method and also maximumangular displacement of this signal combination with respect to anotherusing the same opening for the second signal may be realized.Auto-transformer unit 703 may be located remotely with respect to thesignal pick-01f points and may be conveniently situated in proximity tothe radio equipment proper. Again, coupling capacitors 701 and 702 areseries connected to the input lead so as to reduce the inductivereactance or impedance of the lead-in wires and, in particular, ofauto-transformer unit 703. Additional or substituted capacitors 704 and705 may be utilized in the output of the coupler circuit if desired.

In Figure 8, window 800 is bounded by window frame 801, points 802 and803 of which are electrically connected to points 804 and 805,respectively, of conductive sheath 806. Inner conductor 807 ofconductive sheath 806 is connected to point 808 on Window frame 801 andis routed through conductive sheath 806 to couple to capacitor 809 theremaining side of which is coupled to junction point 810 via conductor811. Junction point 810 is directly connected to point 808 and also topoint 812 on outer sheath 813. Conductor 814 is routed from point 802 onwindow frame 801 to capacitor 815 the opposite side of which isconnected to conductor 816 which is routed through outer sheath 813 toconstitute, ultimately, inner conductor 816 of output coaxial cable 817.Coaxial shield 818 of coaxial cable 817 is directly connected to outersheath 813. Point 819 on outer sheath 813 is directly connected throughpoint 821 to point 805 on conductive sheath 806. Conductor 820 isconnected between junctions 821 and 822. Ferrite sheath 823 enclosesconductors 811, 816 and 820, as shown, to increase the inductivereactance thereof and also to prevent the loading thereof by thesurrounding low impedance conductive mass.

The circuit in Figure 8 operates as follows. Assume point 802 and point803 (to a lesser degree) are increasing positively in potential withrespect to point 808 on window frame 801. An in-phase voltage will beinduced in conductor 807 by current flow in conductive sheath 806 sothat conductor 811 will be positive at junction 810 with respect to theassociated sideof capacitor 809. A voltage of like polarity will appearacross conductor, 820 by reason of the voltage difference, betweenpoints 802 and 803 on window frame 801. The voltages of conductors 811and 820 combine to induce an increased voltage in conductor 816 in theregion of ferrite sheath 823. This induced voltage will be in phase withthe voltage induced in conductor 816 in the region of outer sheath 813by the increased potential difference across outer sheath 813 so as toprovide a greatly increased voltage difierence between inner conductor816 and coaxial shield 818 of output coaxial cable 817. Again,capacitors 809 and 815, together with capacitor 824, if required, areemployed to lower the impedance ofthe coupling circuit and hence toincrease the sensitivtiy of the system.

In Figure 9 (which is in the main similar to Figure 1) an externaldriving voltage is obtained from another portion of the car as, forexample, wheel well 900 which adds to the voltage derived from window901 so as to add to the final voltage output existing between shield 902and inner conductor 903 of coaxial cable 904 and also assists indisplacing the signal at a greater angle than could be attained by usingsignals from the one openingalone; Also, capacitor 905 and capacitor 906(if necessary) may be utilized to counterbalance the inductivereactance' exhibited by the coupling circuit. As with the cables in theother embodiments, cable 907 will have a lowcharacteristic impedance.Again, ferrite sheath 908 in addition to increasing the impedance ofconductors 903 and 909 therewithin magnetically shields conductors 909and 910 from extraneous loading and other influences.

The embodiment of Figure 10 is similar to the circuit of Figure 6, inthat the same dual drive system is utilized in'the principal signalpick-up circuitry associated with.

discontinuity 1000 in Figure 10 as was utilized in connection with thediscontinuity in Figure 6. However, in Figure 10 dual pick-up points arealso utilized along auxiliary discontinuity 1001. The signals from theauxiliary discontinuity 1001 are combined in phase with those from theprincipal discontinuity 1000 through conductors that are common to bothtransformer sections 1002 and 1003. Extensions of inner conductors 1004and 1005 form the common links between sections 1002 and 1003 thusproducing an additive combination of the signals in both circuits.Impedance lowering condensers 1006, 1007, 1008, 1009, 1010 and 1011 maybe added to permit series connection of the transformer sections 1002and 1003 into the input tuning circuits of associated radio apparatus.

It should be noted that although throughout this discussion the ferritesheath has been described as surrounding the signal conductors, it isequally feasible to surround the adjacent conductive material or inserttherewitlu'n ferrite material so as to eliminate any loading of adjacentsignal carrying wiresand so as to raise the impedance of such conductivematerial and attain higher voltages between separated points thereon.

Various departures may be made from the embodiments shown in the variousfigures without departing from the scope of this invention. For example,instead of crossing the window or opening the lead wires may be suitablyshielded from external influences and routed along the periphery of thewindow. Any auto-transformer device disclosed may employ one or moreconductor loops depending upon the particular design of the couplingcircuit that is needed. In addition, a single or dual driving voltagemay be obtained from a remote part of the automobile or other metal massrelative to the radio receiver or transmitter, such as from a wheel wellor other enclosed discontinuity, and the wires be subsequently routedthrough a low impedance cable and capacitance coupled to the radio setor an additional autotransformer device. Auto-transformers in thevarious embodiments may or may not be center tapped, as is desired.Rather than take only one space-phased signal from two displaced pointson the conductive boundary of a discontinuity which the accompanyingfigures suggest, two or more signals from additional appropriatelydisplaced, pick-off points on the same boundary may be obtained andsubsequently combined to insure optimum omnidirectivity of the antennasystem. All of the embodiments presented have proven or appear todemonstate the soundness of utilizing the concept of choosing at leasttwo points from the boundary of at least one conductive mass betweenwhich points there exists a potential difierence by virtue of theirbeing so displaced as to provide the desired angulardisplacement ofsignals, loopingconductive wires coupled to such points so as togenerate an auto-transformer effect, and employing coupling capacitorsto counterbalance the inductive reactance of the coupling circuit.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its} broader aspects, and, therefore, the aim in theappendedclaims is to cover all such changes and modifications as fallwithin the true spirit and scope of this invention.

1 claim:

1. An antenna system including: a conductive struc of said edge at aplurality of points spaced along its length whereby said part of saidprimary portion attains a potential gradient along its lengthcorresponding to the gradient of said contiguous firstportion of saidedge; an exciter wire and a capacitor connected in series and coupledbetween a second portion of said edge remote from said first portion andsaid primary portion of said auto-transformer, said secondary portionbeing adapted for coupling to radio apparatus.

2. Apparatus according to claim 1 in which said part of said primaryportion comprises an electrically conductive sheath.

3. Apparatus according to claim 1 in which said second portion of saidconductive edge is onthe opposite side of said area from said firstportion of said edge.

4. Apparatus according to claim 2vin which said autotransformerincludes, in addition to said sheath, a first conductor passing throughsaid sheath at least once and having an input terminal and an outputterminal; a second conductor in close proximity with a portion of saidfirst conductor and coupled between said first conductor input terminaland said second point on said conductive sheath; and a sheath of highmagnetic permeability in close proximity to said first and secondconductors.

5. Apparatus according to claim 1 in which the magnitude of saidcapacitor is chosen to producev series resonance of said exciter wire inthe range of operatingfrequencies of said radio apparatus. v

6. Apparatus according to claim 4 in which said exciter wire is shieldedin the region proximate to said nonconductive area.

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